Method and device for controlling an exhaust gas post-treatment

ABSTRACT

In a method and device for controlling an exhaust gas post-treatment for an internal combustion engine with at least one cylinder (Z 1 -Z 4 ) and one combustion chamber ( 26 ) and one exhaust gas tract ( 14 ) in which is disposed an SCR catalyst ( 34 ), a humidity parameter (HDT EXH) of an exhaust gas in the exhaust gas tract ( 14 ) is determined upstream of the SCR catalyst ( 34 ) of the internal combustion machine. A control signal for an actuator for introducing ammonia into the exhaust gas is determined as a function of the humidity parameter (HDT_EXH) of the exhaust gas, and the actuator is adjusted accordingly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/EP2009/057499 filed Jun. 17, 2009, which designates the United States of America, and claims priority to German Application No. 10 2008 036 418.5 filed Aug. 5, 2008, the contents of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The invention relates to a method and a device for controlling an exhaust gas post-treatment process for an internal combustion engine having an SCR catalytic converter.

BACKGROUND

Ever more stringent statutory regulations regarding permissible emissions of harmful substances from motor vehicles in which internal combustion engines are arranged make it necessary to keep the emissions of harmful substances as low as possible during operation of the internal combustion engine. This can be done on the one hand by reducing the emissions of harmful substances which are produced during combustion of the air/fuel mixture in the respective cylinder of the internal combustion engine. On the other hand, exhaust gas post-treatment systems which convert the emissions of harmful substances that are produced during combustion of the air/fuel mixture in the respective cylinder into harmless substances are employed in internal combustion engines. For this purpose, catalytic converters are employed which convert carbon monoxide, hydrocarbons and nitrogen oxides into harmless substances. Both exerting a specific influence on the production of emissions of harmful substances during the combustion process and also the conversion of the pollutant components with a high level of efficiency by an exhaust gas catalytic converter require that an extremely precise air/fuel ratio be set in the respective cylinder.

In this context it is necessary to ensure that the components of the exhaust gas post-treatment system also function in the desired manner and that faults are reliably detected over an extended operating life.

With regard to a lean running gasoline engine and with regard to a diesel internal combustion engine, nitrogen oxides can be produced during a combustion process in a combustion chamber of the corresponding internal combustion engine. The nitrogen oxides produced then form part of an exhaust gas from the internal combustion engine. In order to reduce the nitrogen oxide content of the exhaust gas, a reducing agent can be metered into exhaust gas tract of the internal combustion engine, by means of which the nitrogen oxides are enabled to react in an SCR catalytic converter to form harmless nitrogen and water. Ammonia is preferably used as the reducing agent. The ammonia can be obtained by heating a complex salt and is metered in gaseous form into the exhaust gas tract. As an alternative, an aqueous urea solution can be metered into the exhaust gas tract, which aqueous urea solution then at least partially hydrolyzes on account of the heat in the exhaust gas tract to form ammonia which reacts with the nitrogen oxides of the exhaust gas in the SCR catalytic converter. If the nitrogen oxides are not completely reduced, they contribute to pollution of the environment. If an excess of ammonia is metered in and the ammonia exits from exhaust gas tract, then this results in a considerable odor nuisance in an area around the internal combustion engine.

SUMMARY

According to various embodiments, a method and a device for controlling an exhaust gas post-treatment for an internal combustion engine can be created, which contribute to a particularly advantageous reduction of the harmful emission content of the exhaust gas of the internal combustion engine.

According to an embodiment, in a method for controlling an exhaust gas post-treatment process for an internal combustion engine having at least one cylinder with a combustion chamber and an exhaust gas tract in which is arranged an SCR catalytic converter,—a parameter is determined for a water content of an exhaust gas in the exhaust gas tract upstream of the SCR catalytic converter of the internal combustion engine, and—depending on the parameter for the water content of the exhaust gas a control signal is determined for an actuator for introducing ammonia into the exhaust gas and the actuator is set.

According to a further embodiment, the parameter for the water content of the exhaust gas can be determined depending on the air humidity content of the ambient air fed to the internal combustion engine. According to a further embodiment, the parameter for the water content of the exhaust gas can be determined depending on the temperature of the ambient air fed to the internal combustion engine. According to a further embodiment, the air humidity content and/or the temperature can be determined by means of one or more sensors, the measurement signal from which is representative or the measurement signals from which are representative of the air humidity content and/or the temperature of the ambient air fed to the internal combustion engine. According to a further embodiment, a setting of the actuator may have an effect on an ammonia mass which is fed to the SCR catalytic converter.

According to another embodiment, a device for controlling an exhaust gas post-treatment process for an internal combustion engine having at least one cylinder with a combustion chamber and an exhaust gas tract in which is arranged an SCR catalytic converter, is designed in order to determine a parameter for a water content of an exhaust gas in the exhaust gas tract upstream of the SCR catalytic converter of the internal combustion engine, and depending on the parameter for the water content of the exhaust gas, to determine a control signal for an actuator for introducing ammonia into the exhaust gas and to set the actuator.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be described in detail in the following with reference to schematic drawings.

In the drawing:

FIG. 1 shows an internal combustion engine having a control device, and

FIG. 2 shows a block diagram for a method for controlling an exhaust gas post-treatment process for the internal combustion engine.

Elements having the same construction or function are identified by the same reference characters in all the figures.

DETAILED DESCRIPTION

According to various embodiments, in a method and a device for controlling an exhaust gas post-treatment for an internal combustion engine having at least one cylinder with a combustion chamber and an exhaust gas tract in which is arranged an SCR catalytic converter, a parameter is determined for a water content of an exhaust gas in the exhaust gas tract upstream of the SCR catalytic converter of the internal combustion engine, and depending on the parameter for the water content of the exhaust gas a control signal is determined for an actuator for introducing ammonia into the exhaust gas and the actuator is set.

On account of the water contained in the exhaust gas, water can become deposited in the SCR catalytic converter. As a result, a deviation of the actual timing profile of the catalyst temperature from a timing profile of the catalyst temperature as would occur without water deposited in the SCR catalytic converter may arise.

The advantage of taking into consideration the water content of an exhaust gas in the exhaust gas tract upstream of the SCR catalytic converter consists is the fact that the water/humidity content in the SCR catalytic converter can be taken into consideration with regard to the injection quantity and the injection timing point of the reducing agent to be added. If necessary, it is possible to introduce suitable heating measures for the catalytic converter. It is thus possible to more easily avoid NOx emissions. Furthermore, it is possible to avoid a blockage of the SCR catalytic converter resulting from a high water/humidity content in the SCR catalytic converter. In addition, specifications can be made relating to ageing behavior of the SCR catalytic converter dependent on the humidity penetration.

In an embodiment, the parameter for the water content of the exhaust gas is determined depending on the humidity content of the ambient air fed to the internal combustion engine. A precise determination of the water/humidity content in the SCR catalytic converter is thus possible.

In a further embodiment, the parameter for the water content of the exhaust gas is determined depending on the temperature of the ambient air fed to the internal combustion engine. This has the advantage that a precise determination of the humidity content of the ambient air and thus of the exhaust gas is possible.

In a further embodiment, the air humidity content and/or the temperature are/is determined by means of one or more sensors, the measurement signal from which is representative or the measurement signals from which are representative of the air humidity content and/or the temperature of the ambient air fed to the internal combustion engine. This makes it possible to regulate the exhaust gas post-treatment whilst taking into consideration the water/humidity content in the SCR catalytic converter by means of sensors which are simply built in.

In a further embodiment, a setting of the actuator has an effect on an ammonia mass which is fed to the SCR catalytic converter. This constitutes a simple possible means of metering the ammonia mass in a suitable manner.

FIG. 1 shows an internal combustion engine having an intake tract 10, an engine block 12, a cylinder head 13 and an exhaust gas tract 14. The intake tract 10 preferably comprises a throttle valve 15 and an induction manifold 17. The induction manifold 17 leads to a cylinder Z1 in the intake port into a combustion chamber 26 of the engine block 12. The engine block 12 comprises a crankshaft 18 which is coupled by way of a connecting rod 20 to a piston 21 in the cylinder Z1.

The cylinder head 13 comprises a valve operating mechanism having a gas inlet valve 22 and a gas outlet valve 24. The cylinder head 13 also comprises an injection valve 28 and a spark plug 30. Alternatively, the injection valve 28 can also be arranged in the induction manifold 17.

An SCR catalytic converter 34 is arranged in the exhaust gas tract 14 in order to reduce NOx.

Also associated with the internal combustion engine is a control device 35, with associated sensors which sense different measurement variables and can in each case determine the value of the measurement variables. The control device 35 is designed in order to determine correcting variables, depending on at least one of the measurement variables, which correcting variables can then be converted into one or more control signals for controlling actuators by means of corresponding final control elements. The control device 35 is here referred to as a device for controlling an exhaust gas post-treatment process.

The actuators are for example the throttle valve 15, the gas inlet and gas outlet valves 22, 24, the injection valve 28 or the spark plug 30.

The sensors comprise a pedal position sensor 36 which senses an accelerator pedal position of an accelerator pedal 38. The internal combustion engine also has a humidity sensor 40 which is arranged upstream of the throttle valve 15 where it senses an air humidity content of the intake air. A temperature sensor 42 upstream of the throttle valve 15 senses an intake air temperature.

Arranged downstream of the SCR catalytic converter 34 is a NOx sensor 44 which senses a NOx concentration of the exhaust gas.

Depending on the embodiment, any desired subset of the aforementioned sensors may be present, or additional sensors may also be present.

In addition to the cylinder Z1, further cylinders Z2 to Z4 are preferably also provided, to which corresponding actuators and, where applicable, sensors are likewise assigned.

In order to carry out the method for controlling an exhaust gas post-treatment process for an internal combustion engine, a program can be stored in a program memory in the control device 35 and executed during operation of the internal combustion engine.

The program is illustrated in FIG. 2.

The figure shows a temperature model 100 for calculating the temperature of the exhaust gas of the internal combustion engine from an exhaust gas mass flow EXH_MASS_FLOW, an exhaust gas temperature TEMP_TUR_UP upstream of a turbine of the internal combustion engine, and a total injection quantity MF_TOT of fuel. A modeled exhaust gas temperature TEMP_EXH_MDL is determined by means of the temperature model 100 for the exhaust gas of the internal combustion engine.

Furthermore, a measured exhaust gas temperature TEMP_EXH_MES is determined and compared in a comparison block 102 with the modeled exhaust gas temperature TEMP_EXH_MDL, as a result of which an exhaust gas temperature TEMP_EXH is defined in a suitable manner as an output variable from the comparison block 102.

In a humidity model 104 of the exhaust gas of the internal combustion engine, a modeled water content HDT_EXH_MDL of the exhaust gas is defined from an air temperature AIR_TEMP of the ambient air, an air humidity content AIR_HDT of the ambient air, an injection quantity MF_CYL into a cylinder, a total air charge MASS_GAS_CYL in the cylinder and a combustion efficiency level CMB_EFF of the internal combustion engine.

The air humidity content AIR_HDT of the ambient air is preferably sensed by the humidity sensor 40, the air temperature AIR_TEMP of the ambient air is preferably sensed by the temperature sensor 42 upstream of the throttle valve 15. In alternative embodiments of the method for controlling the exhaust gas post-treatment process, the air humidity content AIR_HDT and the air temperature AIR_TEMP of the ambient air can also be determined by means of an empirical model of weather data.

Furthermore, a correction factor FAC_EGR_COR of the exhaust gas recirculation is determined from a mass flow MASS_EGR of the exhaust gas recirculation by means of a first characteristic diagram 106 and a water content HDT_EXH of the exhaust gas is determined in a first multiplier 108 together with the modeled water content HDT_EXH_MDL of the exhaust gas determined from the humidity model 104 of the exhaust gas.

As a result of the determination of the parameter for the water content HDT_EXH of the exhaust gas dependent on the air humidity content AIR_HDT and of the temperature AIR_TEMP of the ambient air fed to the internal combustion engine, a precise determination of the water content HDT_EXH of the exhaust gas is possible.

In a temperature model 110 of the SCR catalytic converter 34, depending on the exhaust gas temperature TEMP_EXH, the exhaust gas mass flow EXH_MASS_FLOW, a vehicle speed VS, the temperature AIR_TEMP of the ambient air fed to the internal combustion engine, a heat capacity C_CAT and a catalyst volume VOL_CAT of the SCR catalytic converter 34, a modeled catalyst temperature TEMP_CAT_MDL is determined and fed to a second multiplier 114. The value determined for the water content HDT_EXH of the exhaust gas is fed to a second characteristic diagram 112 and a correction factor FAC_HDT_COR for the humidity content is determined from this and likewise fed to the second multiplier 114.

In an already known manner, a modeled urea injection quantity UREA_INJ_MDL for the injection of urea into the exhaust gas in the exhaust gas tract 14 is determined by means of a urea injection model 116, amongst other things, from the exhaust gas mass flow EXH_MASS_FLOW and a NOx content NOX in the exhaust gas and fed to a third multiplier 120.

From the values fed to the multiplier 114, a catalyst temperature TEMP_CAT is determined and fed to a third characteristic diagram 118. A correction factor UREA_INJ_COR for the urea injection quantity is determined by means of the third characteristic diagram 118 and likewise fed to the third multiplier 120.

From the values fed to the multiplier 120, the injection quantity UREA_INJ of urea into the exhaust gas tract 14 upstream of the SCR catalytic converter 34 is determined.

By using this method it is possible to take into consideration the actual catalyst temperature TEMP_CAT for controlling the exhaust gas post-treatment process whilst taking into consideration the water content HDT_EXH in the exhaust gas and/or condensate in the SCR catalytic converter 34. The injection quantity and the injection timing point of the reducing agent to be added, in other words the urea solution in particular, can thus be precisely determined. Urea or another reducing agent can be added to the exhaust gas upstream of the SCR catalytic converter precisely at the time when a specified catalyst temperature TEMP_CAT is actually reached. A possibly unnecessary use of urea or another reducing agent prior before the specified catalyst temperature TEMP_CAT is reached can thus be avoided. It is thus quite possible to avoid emissions of ammonia or NOx from the SCR catalytic converter 34. In particular, it is also possible to avoid the functional integrity of the SCR catalytic converter 34 being impaired by a high water or humidity content. Since a deposit of water or humidity in the SCR catalytic converter 34 can lead to additional ageing of the SCR catalytic converter 34, this method additionally makes it possible to precisely determine the ageing of the SCR catalytic converter 34. 

1. A method for controlling an exhaust gas post-treatment process for an internal combustion engine having at least one cylinder with a combustion chamber and an exhaust gas tract in which is arranged an SCR catalytic converter, the method comprising: determining a parameter for a water content of an exhaust gas in the exhaust gas tract upstream of the SCR catalytic converter of the internal combustion engine, and depending on the parameter for the water content of the exhaust gas, determining a control signal for an actuator for introducing ammonia into the exhaust gas and the actuator is set.
 2. The method according to claim 1, wherein the parameter for the water content of the exhaust gas is determined depending on the air humidity content of the ambient air fed to the internal combustion engine.
 3. The method according to claim 1, wherein the parameter for the water content of the exhaust gas is determined depending on the temperature of the ambient air fed to the internal combustion engine.
 4. The method according to claim 2, wherein at least one of the air humidity content and the temperature are/is determined by means of one or more sensors, the measurement signal from which is representative or the measurement signals from which are representative of at least one of the air humidity content and the temperature of the ambient air fed to the internal combustion engine.
 5. The method according to claim 1, wherein a setting of the actuator has an effect on an ammonia mass which is fed to the SCR catalytic converter.
 6. A device for controlling an exhaust gas post-treatment process for an internal combustion engine having at least one cylinder with a combustion chamber and an exhaust gas tract in which is arranged an SCR catalytic converter, whereby the device is configured to, determine a parameter for a water content of an exhaust gas in the exhaust gas tract upstream of the SCR catalytic converter of the internal combustion engine, depending on the parameter for the water content of the exhaust gas, to determine a control signal for an actuator for introducing ammonia into the exhaust gas and to set the actuator.
 7. The device according to claim 6, wherein the parameter for the water content of the exhaust gas is determined depending on the air humidity content of the ambient air fed to the internal combustion engine.
 8. The device according to claim 6, wherein the parameter for the water content of the exhaust gas is determined depending on the temperature of the ambient air fed to the internal combustion engine.
 9. The device according to claim 7, wherein at least one of the air humidity content and the temperature are/is determined by means of one or more sensors, the measurement signal from which is representative or the measurement signals from which are representative of at least one of the air humidity content and the temperature of the ambient air fed to the internal combustion engine.
 10. The device according to claim 6, wherein a setting of the actuator has an effect on an ammonia mass which is fed to the SCR catalytic converter.
 11. A motor vehicle, comprising: an internal combustion engine having an intake tract, an engine block, a cylinder head and an exhaust gas tract, an SCR catalytic converter arranged in the exhaust gas tract; a control device; sensors associated with said control device, said sensors sensing different measurement variables, wherein the control device is configured to determine correcting variables depending on at least one of the measurement variables, which correcting variables can be converted into one or more control signals for controlling actuators by means of corresponding final control elements; and wherein the control device is further configured: to determine a parameter for a water content of an exhaust gas in the exhaust gas tract upstream of the SCR catalytic converter of the internal combustion engine, depending on the parameter for the water content of the exhaust gas, to determine a control signal for an actuator for introducing ammonia into the exhaust gas and to set the actuator.
 12. The motor vehicle according to claim 11, wherein the intake tract comprises a throttle valve and an induction manifold, wherein the induction manifold leads to a cylinder in the intake port into a combustion chamber of the engine block.
 13. The motor vehicle according to claim 12, wherein the engine block comprises a crankshaft which is coupled by way of a connecting rod to a piston in the cylinder, and wherein the cylinder head comprises a valve operating mechanism having a gas inlet valve and a gas outlet valve.
 14. The motor vehicle according to claim 13, wherein the cylinder head also comprises an injection valve and a spark plug.
 15. The motor vehicle according to claim 11, wherein the actuators are selected from the group consisting of a throttle valve, a gas inlet valve, a gas outlet valve, an injection valve, and a spark plug.
 16. The motor vehicle according to claim 11, wherein the sensors comprise at least one of: a pedal position sensor which senses an accelerator pedal position of an accelerator pedal, a humidity sensor which is arranged upstream of the throttle valve, a temperature sensor upstream of the throttle valve, an NOx sensor arranged downstream of the SCR catalytic converter.
 17. The motor vehicle according to claim 11, wherein the parameter for the water content of the exhaust gas is determined depending on the air humidity content of the ambient air fed to the internal combustion engine.
 18. The motor vehicle according to claim 11, wherein the parameter for the water content of the exhaust gas is determined depending on the temperature of the ambient air fed to the internal combustion engine.
 19. The motor vehicle according to claim 17, wherein at least one of the air humidity content and the temperature are/is determined by means of one or more sensors, the measurement signal from which is representative or the measurement signals from which are representative of at least one of the air humidity content and the temperature of the ambient air fed to the internal combustion engine.
 20. The motor vehicle according to claim 11, wherein a setting of the actuator has an effect on an ammonia mass which is fed to the SCR catalytic converter. 